The term drumhead refers to a type of removable sign that was prevalent on North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

n railroads

Rail transport

Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

 of the first half of the 20th century. The sign was mounted at the rear of passenger trains, and consisted of a box with internal illumination that shone through a tinted panel bearing the logo

Logo

A logo is a graphic mark or emblem commonly used by commercial enterprises, organizations and even individuals to aid and promote instant public recognition...

 of the railroad or specific train. Since the box and the sign were usually circular in shape and resembled small drums, they came to be known as drumheads.

Railroad drumheads were removable so that they could be mounted on different passenger cars (usually on the rear of observations

Observation car

An observation car/carriage/coach is a type of railroad passenger car, generally operated in a passenger train as the last carriage, with windows on the rear of the car for passengers' viewing pleasure...

), as needed for specific trains.